1. Field of the Invention
The present invention relates to storage-stable urethane acryls and to a method for their production.
2. Description of the Prior Art
Efficient, unsaturated resins hardenable through UV radiation, for example, urethane acryls, can be produced, for example, by the reaction of polyols with isocyanates with the addition of unsaturated, for example, olefinic final groups. Such products are hardenable to dry plastic films by adding for example, aromatic ketones and their derivatives, so-called photoinitiators, by means of UV radiation of a wave length of 200-400 nm depending on the thickness of the layer within periods of 0.1-10 seconds.
The properties of the final products result, in an actually known manner, from structurally adjustable conjugations of polyol components with the respective isocyanates and the used olefin structures. In order to produce final products meeting high requirements and being stable to light, the use of aliphatic isocyanates is necessary.
Combinations of polyols especially of oxyesters, with sterically hindered cycloaliphatic diisocyanates, their adducts and derivatives, particularly on the basis of isophorondiisocyanate (IPDI) in accordance with the following structural formula prove to be particularly efficient with regard to light, heat and oxidation resistance: ##STR1##
For the production of UV-hardenable acryl urethane resins, it involves relatively few problems to transform bifunctional polyols with diisocyanates and olefinic reactants into moderately viscous, storage-stable acryl urethanes. By doing so, initially the bifunctional polyol is added drop by drop to a suitable reactive diluent which contains already the diisocyanate component with or without catalyst, after a few hours the NCO content is determined and, subsequently, hydroxyalkylacrylate is added with or without catalyst for the production of a largely NCO-free urethane acryl resin.
However, it is also desirable to use tri and tetrafunctional polyols in accordance with the property picture and efficiency.
However, in accordance with the known process, it involves considerable difficulties to carry out the conjugation of polyfunctional, i.e., tri and tetrafunctional oxyesters, with IPDI or other diisocyanates and olefinic reactants since highly viscous products are formed with a very low storage stability. Furthermore, the storage stability of such resins is impaired with the presence of enolizable aromatic activators.
However, resins are required whose viscosity can be controlled and which have a good storage stability. It is actually possible to produce in a known manner storage-stable trifunctional oxyester reaction products with, for example, IPDI but they supply highly viscous final products of a deficient stability after the acrylization. Still greater difficulties are encountered when producing storage-stable tetrafunctional urethane acryl resins which present highly valuable structural elements within the UV-hardenable resins.